Igneous Rock (Volcanic Glass)

Scoria (vesicular volcanic rock)

Basaltic scoria; chiefly plagioclase, pyroxene, olivine, and iron-rich volcanic glass

Basalt River Cobble

Basalt (Mafic volcanic rock)

Quartz Vein in Host Rock

Silicon Dioxide (SiO2)

Basalt

Basalt

Weathered quartz-bearing rock, possibly porphyritic rhyolite

Likely altered rhyolite or dacite containing quartz and feldspar; exact identification requires testing

Quartz crystals on Basalt

SiO2 (Quartz) on Mafic Igneous Rock (Basalt)

Scoria (Lava Rock)

Vesicular Basalt / Scoria

Tumbled dark volcanic rock, possibly basalt

Basalt; commonly composed of plagioclase feldspar, pyroxene, and minor olivine or magnetite

Tumbled gray stone, likely quartzite or fine-grained basalt

Provisional identification: quartzite (mostly microcrystalline SiO₂) or basalt (plagioclase–pyroxene aggregate)

Pumice

Pumice (Vesicular Felsic Igneous Rock)

Vesicular volcanic rock, likely pumice

Pumice; highly vesicular volcanic glass, commonly rhyolitic to dacitic in composition

Vesicular volcanic rock, likely pumice or scoria

Pumice/scoria; predominantly volcanic glass with plagioclase, pyroxene, and/or olivine

Amethyst (Rough)

Silicon Dioxide with iron impurities (SiO2)

Basalt

Extrusive Igneous Rock

Black volcanic glass (likely obsidian)

Obsidian; predominantly rhyolitic volcanic glass composed chiefly of amorphous SiO₂

Rounded gray river pebble, likely basalt or andesite

Fine-grained mafic to intermediate volcanic rock; commonly basalt (plagioclase ± pyroxene/olivine)

Pumice

Pumice (volcanic glass with vesicular texture)

Red vesicular volcanic rock, likely scoria

Basaltic scoria; predominantly plagioclase, pyroxene, olivine, and volcanic glass

Basalt Pebble

Mafic Igneous Rock

Porphyry (Porphyritic Basalt / Andesite)

Porphyritic Igneous Rock

Weathered, vesicular volcanic rock (likely pumice/scoria)

Pumice or scoriaceous basalt; composition likely volcanic glass with feldspar, pyroxene, and minor iron oxides

Pumice or vesicular volcanic rock

Pumice; chiefly volcanic glass (silica-rich, composition commonly rhyolitic to dacitic)

Olivine in Basalt (Peridot)

Magnesium Iron Silicate (Mg, Fe)2SiO4 in Vesicular Basalt

Dark volcanic rock, likely basalt

Basalt; fine-grained mafic volcanic rock composed mainly of plagioclase, pyroxene, and commonly olivine

Pumice

Vesicular Rhyolite or Andesite (Amorphous volcanic glass)

Amethyst

Amethyst (Silicon Dioxide - SiO2)

Pumice

Pumice (a highly vesicular amorphous volcanic glass)

Dark igneous rock, likely basalt

Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine or iron-titanium oxides

Basalt (Weathered)

Mafic Igneous Rock

Basalt

Extrusive Igneous Rock

Vesicular volcanic rock, likely pumice or scoria

Pumice (highly vesicular rhyolitic–dacitic volcanic glass) or scoria (vesicular basaltic rock)

Light-colored igneous rock, likely pumice or vesicular rhyolite

Primarily silica-rich volcanic glass and feldspar; exact identification is uncertain from the photograph

Basalt

Basalt

Pumice

Pumice (volcanic glass formed of highly vesicular rough textured rock)

Mahogany Obsidian

Volcanic Glass with Hematite/Magnetite inclusions

Pumice

Pumice (Volcanic glass with vesicular texture)

Pumice

Pumice (a highly vesicular volcanic glass)

Basalt

Extrusive Igneous Rock

Basalt

Extrusive Igneous Rock

Basalt

Extrusive igneous rock

Snowflake Obsidian

Volcanic Glass with Spherulite Inclusions (primarily SiO2)

Mahogany Obsidian

Volcanic Glass (predominantly SiO2 with Fe2O3 inclusions)